The middle ear comprises the malleus (hammer), the incus (anvil), and the stapes (stirrup). They form a short bony chain spanning between the external ear and the middle ear. The malleus resembles a club, the incus a premolar tooth, and the stapes a stirrup.
The malleus and the incus have a tightly fitting joint between them. The long process of the incus is bent near its lower end and carries a small bony knob that forms a loose joint with the head of the stapes. The stapes is about 3 millimeters high and weighs slightly less than 3 milligrams. It lies almost horizontally at right angles to the long process of the incus. The footplate of the stapes fits neatly in the oval window, which is one of the two openings in the wall of the bony labyrinth, where it is held in place by the annular ligament.
When sound is transmitted through the ear canal, the malleus, which is attached to the ear drum, moves in and out with the movements of the drum membrane in response to the sound. The incus that is attached to the malleus, moves with the malleus. The stapes that is coupled to the incus does not move in and out of the oval window, but rocks about the lower pole of its footplate as it transmits the vibrations to the inner ear. The footplate of the stapes fits neatly into the oval window, thereby concentrating the sound in a small area.
A disease of the middle ear known as fixation of the stirrup by otosclerosis causes progressive hearing loss in early and middle adult life. Otosclerosis is the abnormal formation of spongy bone in the inner ear that causes the stapes to become immobilized. In its early and actively expanding stage the nodule of the softened bone becomes large enough to reach the oval window containing the footplate of the stirrup. Increasing pressure caused by expanding nodule begins to impede the vibratory movements of the stapes in response to sound striking the drum membrane.
Fixation of the stirrup bone can be corrected surgically by an operation known as stapedectomy. This operation involves the removal of the affixed stirrup bone and replacement by a plastic or wire substitute, such as a TEFLON (registered trademark) piston. The operation restores the vibration characteristics of the chain of tiny bones of the middle ear.
The operation is extremely delicate and difficult since the middle ear bones are the smallest bones of the body. The surgical implantation of a replacement stapes generally uses an instrument called cupforceps or alligator forceps 1 to hold the prosthetic piston, as best shown in FIG. 1. The cup forceps or alligator forceps 1 are held in similar fashion as holding a pair of scissors. This is inherently unstable, since the surgeon is applying closure pressure on the instrument while at the same time trying to position the prosthetic piston in place. This typically causes vibration at the tip of the instrument if the surgeon is inexperienced. Another factor contributing to the difficulty of the operation is that the operation is done through the ear canal with the use of an ear speculum 3 and a microscope, as best shown in FIG. 1. Because the tip of the cupforceps is typically thick in relation to the prosthetic piston, and because of the narrow field of the operation, it is difficult to see the prosthetic piston tip for accurate implantation into the top of the footplate and for attaching to the lenticular process of the incus. This difficulty is highlighted in FIG. 1, which is a view into the ear canal through the ear speculum 3.
There is therefore a need for a novel instrument that will resolve the above-mentioned difficulties.